The invention concerns a novel catalyst for the polycondensation of diisocyanates, in particular the (cyclo)trimerisation of diisocyanates.
A large number of catalysts are used for the polycondensation of diisocyanates to produce as a majority trimeric compounds with an isocyanurate and/or biuret and/or allophanate unit.
Mention may be made of catalysts of basic type such as tertiary amines described in DE 951 168, derivatives of alkali or alkaline earth metals such as hydroxide, carbamate, alcoholate, etc, described in FR 1 190 065, quaternary ammonium hydroxides described in FR 1 204 697, FR 1 566 256, EP 3765 and EP 10589, catalysts with an ethylene-imine group described in FR 1 401 513 and FR 2 230 642, the Mannich bases in general obtained from phenol, aldehyde and secondary amine described in FR 2 290 459 and FR 2 332 274, phosphines described in FR 1 510 342, FR 2 023 423 and DE 19 347 63 and the aminosylilated derivatives such as monoaminosilanes, diaminosilanes, silylureas and silazanes described in EP 57653.
Those catalysts generally make it possible to obtain a polycondensation product having a satisfactory proportion of trimers.
U.S. Pat. No. 3,736,298 describes a process for the trimerisation of polyisocyanates using a double alcoholate of metals selected from the transition metals of groups III-A, IV-A and V-A, alkali metals and alkaline earth metals, more particularly a complex of alkali or alkaline earth metal of a polyvalent metal alcoholate.
The catalyst is added at ambient temperature (10-40xc2x0 C.) to the reaction medium containing the isocyanate compounds and causes brutal autogenous exothermy which is not controllable. The temperature can thus reach and even exceed 200xc2x0 C. The product obtained at the end of the reaction is a polyisocyanurate compound which is not clearly defined. Moreover, having regard to the exothermy factor and the autocatalytic character of the reaction, it is difficult to develop such a method on an industrial scale. Control of the method is an essential parameter insofar as it makes it possible to reproducibly guarantee a well-defined composition and targeted properties such as products of controlled viscosity, in particular products of very low viscosity.
GB 1 386 399 describes a method for the preparation of isocyanurate polymers by the reaction of isophorone diisocyanate and a catalytic amount of alkali metal phenolate.
Moreover H. Sugimoto and S. Inouxc3xa9 describe in Macromol. Rapid Commun., 17, No 1, January 1996, pages 1-7, the use of lanthanum isopropylate and other lanthanide isopropylates as an anionic initiator for the polymerisation of hexylisocyanate to obtain poly(hexyl isocyanate) of very high molecular weight. The reaction is conducted at low temperatures (xe2x88x9278xc2x0 C.). The document also mentions that at ambient temperature the cyclic trimer is the only reaction product.
In addition it is indicated that the polymerisation of isocyanates carrying secondary and tertiary alkyl groups does not take place.
Ikeda et al (Pure Applied Chem. A 3410), pages 1907-1920 (1997) also describe the polymerisation of monoisocyanates at ambient temperature by means of alcoholates of lanthanides.
They report that, when n-hexyl isocyanate is reacted with yttrium isopropylate at ambient temperature, the result obtained is a product of high viscosity which solidifies after 10 minutes.
After one hour, when hydrochloric acid in methanol solution is added to the polymerisation mixture at ambient temperature, a white powder precipitates.
By the addition of a hydrochloric solution of that white powder in methanol, the result obtained is a fibrous polymer of a molecular weight of 59,000, which is revealed by infrared analysis to have the structure of nylon-1.
On the other hand, with lanthanum triisopropylate, n-hexylisocyanate results at ambient temperature in cyclic trimer as the sole reaction product.
It has now surprisingly been found that in the presence of alcoholates of rare earths, isocyanates having at least two isocyanate functions reproducibly result, under certain condition in terms of control of the reaction, in a (cyclo)condensation product composed principally of true trimer, namely the product of cyclotrimerisation of the isocyanate comprising a single isocyanurate ring, for a high rate of transformation of the initial isocyanate monomer.
Depending on the rare earth used, it is possible to obtain besides the isocyanurate forms, derivatives of biuret and/or imino-oxadiazinetrione type.
The invention concerns a method for the (cyclo)trimerisation of isocyanates having at least two isocyanate functions, characterised in that it comprises:
a) reacting initial isocyanate monomers having at least two isocyanate functions, optionally in the presence of other monomers reactive with the isocyanate monomers having at least two isocyanate functions, at a temperature of at least 20xc2x0 C., advantageously at least 50xc2x0 C., and lower than 200xc2x0 C., advantageously lower than 150xc2x0 C., in the presence of a compound comprising at least one ligand including an alcoholate function of rare earths,
b) stopping the reaction by inactivating the catalyst, in particular by the addition of a compound selected from a strong acid and a peroxide and mixtures thereof at a rate of transformation of the NCO functions present in the reaction medium of at least 2.5%, advantageously 5%, preferably 6%, and at most 80%, advantageously 70%; and optionally
c) distilling the reaction medium to eliminate the unreacted monomers.
Advantageously the compound comprising at least one ligand including a rare earth alcoholate function is in accordance with the invention an alcoholate of rare earths. The other ligands may comprise other functions such as for example acetylacetonates.
For a definition of elements of rare earths, reference will be made to the Table on page B.208 of the xe2x80x9cHandbook of Chemistry and Physicsxe2x80x9d, Editor Robert C. Weast, 67th Ed.
They comprise the following elements: scandium, yttrium, lanthanum as well as lanthanides (cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, ytterbium and lutetium).
According to the invention it is possible to add a compound comprising a rare earth alcoholate function or a mixture of compounds.
The rare earth alcoholate function may consist of any function obtained by substitution of an alcohol OH group by a rare earth metal.
Mention may be made in particular of propylates, especially isopropylates, in particular isopropylate of the following rare earth elements: Y, Sm, Yb and La.
Methylates, ethylates and butylates of the foregoing elements are also satisfactorily suitable.
Moreover, very good results were obtained with compounds comprising at least one rare earth alcoholate function and a polyalkenylene oxide group, in particular polyethylene oxide or polypropylene oxide.
The preference is for the alcoholates of polyalkylene glycol in which the number of alkylene oxide units is not greater than 20, preferably not greater than 10 and preferably not greater than 5.
The alcoholate groups may also be carried by molecules carrying a plurality of alcoholate functions on the same molecule. By way of example mention may be made of the compounds having two alcohol functions such as glycols, butane-diols, branched glycols such as propylene glycol, triols such as glycerol or trimethylolpropane.
The ligands comprising a rare earth alcoholate function may be identical or different.
It is also possible to use a mixture of alcoholates from two or more rare earths or a mixture of metal alcoholates of which at least one is a rare earth alcoholate. The ligands of those alcoholate mixtures may be identical or different.
The method according to the invention may be used for the cyclotrimerisation of any type of isocyanates or mixture of isocyanates as defined hereinbefore whether they are aliphatic, cycloaliphatic or aromatic, including the prepolymers having terminal isocyanate groups, in particular those described in U.S. Pat. No. 5,115,071, the content of which is incorporated by reference into the present application. It can thus be used for the trimerisation of isocyanates in the presence of various diols, triols or other polyols whose molecular weights are in a wide range, including polyols and aminopolyols comprising polyether and polyester groups, which are used for the production of polyurethane and polyisocyanurate resins.
The diisocyanates are however preferred.
The present invention concerns the (cyclo)trimerisation of compounds carrying at least two isocyanate functions which are designated in the present description by monomer isocyanates.
This may involve isocyanate monomers with a hydrocarbon skeleton exclusively of a nature which is aliphatic, straight-chain, branched or cyclic, or aromatic isocyanates.
Hexamethylenediisocyanate (HDI) may be particularly mentioned as a straight-chain aliphatic monomer.
Mention may also be made of aliphatic monomers in which the hydrocarbon skeleton is branched but the isocyanate functions are carried by primary carbon atoms, for example 2-methyl pentane diisocyanate.
Mention may also be made of monomers in which at least one isocyanate function is in a cycloaliphatic, secondary, tertiary or neopentylic position.
Thus, among such products, those which give excellent results with the catalysts of the invention, unlike other catalysts with which they have only a poor transformation rate, are monomers in which the isocyanate function is carried by a carbon atom which is cycloaliphatic, secondary, tertiary or neopentylic, in particular cycloaliphatic isocyanates. Those monomers are such that at least two isocyanate functions are spaced from the closest ring by at most one carbon and are preferably connected directly to it. In addition those cycloaliphatic monomers advantageously have at least two isocyanate functions carried by secondary, tertiary or neopentylic carbon atoms.
Surprisingly, good results are obtained for isocyanates in which the conformational freedom of the carbon carrying the NCO function is low. The following monomers may be mentioned by way of example:
the compounds corresponding to hydrogenation of the aromatic nucleus or nuclei carrying isocyanate functions of monomers of aromatic isocyanates and in particular TDI (toluene diisocyanate) and diisocyanato-biphenyls, the compound known by the abbreviation H12MDI [4,4xe2x80x2-bis-(isocyanatocyclohexyl)methane], the various BIC [Bis(isocyanato-methylcyclohexane)] and the cyclohexyldiisocyanates which are optionally substituted;
and in particular
norbornanediisocyanate, often referred to by its abbreviation NBDI;
isophoronediisocyanate, or IPDI, or more precisely 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate.
The following may be mentioned as aromatic monomers:
2,4- or 2,6-toluene diisocyanate (TDI);
2,6-4,4xe2x80x2-diphenylmethane diisocyanate (MDI);
1,5-naphthalene diisocyanate (NDI);
tolidine diisocyanate (TODI);
p-phenylene diisocyanate (PPDI).
Mention may also be made of isocyanate compounds comprising more than two isocyanate functions, by way of example mention may be made of 4-isocyanatomethyl-octamethylene-diisocyanate which is also known by the abbreviation TTI or NTI, and the ester of lysine 2-isocyanatoethyl-diisocyanate, also known by the name LTI.
The initial monomers may also be products from the oligomerisation of isocyanates of lower molecular mass, such oligomerisation products bearing isocyanate functions. In that case it is not necessary to separate the non-transformed oligomer from the reaction product formed at the end of the trimerisation reaction.
It is also possible to use mixtures of such isocyanates in the cyclotrimerisation reaction in order to obtain mixed isocyanurate compounds or mixtures of isocyanurates.
In that particular case of mixtures of isocyanates, it is possible to use in part molecules which have only one single isocyanate function. In that latter case the amount of isocyanate functions afforded by that monomeric compound may not represent more than 50% by number of the total of isocyanate functions of the whole of the compounds with isocyanate functions. That monomeric compound with a single isocyanate function may optionally comprise functions which are useful for final application of the composition such as polysiloxane functions, polyether functions, perfluorinated functions, alkoxysilane functions.
The catalyst or the mixture of catalysts is added to the reaction medium with agitation, preferably in the absence of solvent or in a solvent, preferably inert, with respect to the isocyanates of the reaction medium. In the case where the solvent is reactive with respect to the isocyanates, the concentration of catalyst is adjusted in such a way that the amount of solvent is not prejudicial to obtaining the compound for the envisaged application.
The solvent is preferably selected in such a way that its boiling point is higher than the reaction temperature. Mention may be made of aliphatic hydrocarbons such as hexane or aromatic hydrocarbons such as toluene, or again alcohols, in particular ethanol, propanol or isopropanol.
It is however possible to operate under pressure with solvents or gases in the supercritical state. The preference however is to operate in a neutral atmosphere.
The molar ratio of the amount of catalyst/amount of isocyanate functions (NCO) is advantageously at least 5xc2x710xe2x88x925 and at most 5xc2x710xe2x88x922, preferably between 10xe2x88x924and 10xe2x88x922. The amount adopted will depend on the structure of the initial isocyanate and more particularly the hindrance of the isocyanate functions. In general, the more the isocyanate function is hindered, the more the reactivity of the isocyanate decreases and consequently the greater the amount of catalyst used.
When the gases dissolved in the initial isocyanate monomers are eliminated the amount of catalyst can be reduced.
In addition when the gases dissolved in the initial isocyanate monomers are eliminated, the reactivity of the catalysts is improved.
The dissolved gases (CO2, halogenated gases, O2 . . . ) can be eliminated by any known means, in particular by bubbling an inert gas such as nitrogen or argon, or by putting the reaction medium under vacuum.
The reaction is allowed to take place for a period which varies between 30 minutes and 7 hours, preferably between 1 hour and 5 hours.
The polycondensation reaction is stopped at the desired rate of transformation of the isocyanate functions.
To stop the (cyclo)trimerisation reaction, it is possible to add to the reaction medium a compound which destroys the catalyst activity of the rare earth alcoholate functions or their derivative forms as are present in the reaction medium, for example the metallic forms which are complexed with a ligand present in the reaction medium. Advantageously a strong acid or a peroxide is added to the reaction medium.
The term xe2x80x9cstrong acidxe2x80x9d in accordance with the present invention is used to denote an acid whose pKa is 7 at most. Mention may be made in particular of hydrochloric acid, sulphuric acid, paratoluene sulphonic acid or phosphoric acid and its alkyl mono- or diesters, in particular diisopropyl phosphoric acid, with the acids optionally being diluted.
The peroxides which can be employed involve any peroxide corresponding to the definition generally accepted for such compounds, namely an anhydride or oxide compound, containing more oxygen than the normal oxide.
Mention may be made of hydrogen peroxide, diethyl peroxide, dibutyl peroxide or benzoyl peroxide.
Mention may also be made of peracids, in particular peracetic acid or perbenzoic acid as well as percarbonates or again the compounds of the reaction of oxygenated water with an isocyanate.
The strong acid or the peroxide is added in an amount such that it permits the transformation of the metal compound into an unreactive compound, that is to say transformation of an alcoholate into an alcohol and salts of a strong acid.
In general the method will use a molar ratio of strong acid functions (peroxide)/strong base function or metal alcoholate function of between 0.5 and 30, between 0.8 and 10.
The addition of those compounds to the reaction medium also causes the coloring thereof to disappear, being due to the presence of a metal complex, without a harmful effect on the initial isocyanates or the polycondensation products obtained.
In an alternative procedure it is also possible to absorb the catalyst or its derivative forms on a mineral support, for example silica, alumina, or other mineral oxides.
In accordance with an embodiment of the invention the (cyclo)trimerisation reaction is conducted in the presence of a compound having a nitrogen heterocycle with five members having at least two nitrogen atoms.
It has surprisingly been observed that, in the presence of a nitrogenous cyclic compound having at least two nitrogen atoms, the catalysts of the invention made it possible to arrive at a reaction product comprising besides the cyclotrimers with an isocyanurate group, polyisocyanate mono-uretdione compounds which are also referred to as xe2x80x9ctrue dimersxe2x80x9d which are molecules resulting from the condensation of two molecules of monomer isocyanates.
In particular a cyclic nitrogenous compound as defined hereinbefore, when added to a rare earth alcoholate in a molar ratio of cyclic nitrogenous compound/rare earth alcoholate of between 0.1 and 10 and in particular between 0.2 and 5, makes it possible to obtain a reaction product comprising polyisocyanate mono-uretdiones and polyisocyanate mono-isocyanurates in a molar ratio of polyisocyanate mono-uretdiones/polyisocyanate mono-isocyanurates of great than 0.5, in particular greater than 0.6, preferably greater than 0.75, and indeed greater than 1.
The invention thus concerns a method for the preparation of a polyisocyanate composition comprising polyisocyanate trimers, in particular polyisocyanate mono-isocyanurates which are also referred to as true trimers and polyisocyanate dimers, in particular polyisocyanate mono-uretdiones also referred to as true dimers, in which the molar ratio of true polyisocyanate dimers/true polyisocyanate trimers is greater than 0.5, in particular greater than 0.6 and preferably greater than 0.75, which involves effecting polycondensation of isocyanate monomers in the presence of a rare earth alcoholate and a nitrogenous compound comprising a heterocycle with five members, having at least two nitrogen atoms, the molar ratio of cyclic nitrogenous compound/rare earth alcoholate being between 0.1 and 10 and advantageously between 0.2 and 5.
The invention also concerns the use of a compound having a nitrogenous heterocycle with 5 members having at least two nitrogen is atoms to promote the opening/closing reaction of uretidinedione rings formed in a method for catalytic (cyclo)trimerisation, of isocyanate compounds having at least two isocyanate functions, in which the (cyclo)trimerisation catalyst comprises a rare earth alcoholate.
In the present invention the term xe2x80x9cmono-uretdionesxe2x80x9d or xe2x80x9ctrue dimersxe2x80x9d is used to denote the compounds obtained by condensation of two molecules of initial isocyanate monomers comprising a single uretdione ring.
The term xe2x80x9cmono-isocyanuratesxe2x80x9d or xe2x80x9ctrue trimersxe2x80x9d is used to denote the compounds obtained by condensation of three molecules of initial isocyanate monomers comprising a single uretdione ring.
The term xe2x80x9cheavy compoundsxe2x80x9d is used to denote the compounds obtained by the condensation of more than three molecules of isocyanate monomers, in particular the xe2x80x9cbis-trimersxe2x80x9d, the xe2x80x9cbis-dimersxe2x80x9d, the tris-trimers and the xe2x80x9cdimers-trimersxe2x80x9d.
The bis-trimers are polyisocyanate molecules comprising two isocyanurate rings in which the connection between the two isocyanurate rings is ensured by a monomer unit, namely that two isocyanate functions are engaged in each of the isocyanurate rings.
The bis-dimers are polyisocyanate molecules comprising two uretdione rings in which the connection between the two uretdione rings is ensured by a monomer unit, namely that two isocyanate functions are engaged in each of the uretdione rings.
The tris-trimers are higher homologues of the bis-trimers comprising three isocyanurate rings.
In the case where the monomers are diisocyanates, tris-trimers are obtained by polycondensation of seven monomer chains and comprise three isocyanurate rings, two consecutive isocyanurate rings being connected by a monomer unit.
The dimers-trimers are higher homologues of the foregoing compounds comprising an isocyanurate function and a mono-uretidione function.
The nitrogenous pentacyclic compound with five members is advantageously selected from imidazole, triazole, tetrazole and their derivatives comprising one or more substituents, in particular between 1 and 4 substituents according to the nature of the ring.
The substituents may be selected independently of each other from OH, SH, a C1-C4 alkyl group, a C1-C4 hydroxyalkyl group, a C1-C4 aminoalkyl group, a C1-C4 alkylamino group; dialkylamino (each alkyl group having between 1 and 4 carbon atoms), a C1-C4 alkylthio group, a C1-C4 halogenoalkyl group, a C3-C8 cycloalkyl group, a C5-C10 aryl group, a heterocyclic group in which the heterocycle comprises between 2 and 10 carbon atoms and between 1 and 4 heteroatoms which are identical or different selected from O, S and N and the group NR4, R4 being in particular a C1-C4 alkyl group or a C3-C8 cycloalkyl group.
The preference is for the compounds having a non-substituted imidazole nucleus or having an imidazole nucleus carrying a N-alkyl, preferably N-methyl, substituent.
It is generally preferred to add to the reaction medium the catalyst and the nitrogenous cyclic compound simultaneously in a solution of solvent.
As solvents mention may be made of those referred to hereinbefore. It is generally preferred to add the rare earth alcoholate at the same time as the nitrogenous cyclic compound, in particular imidazole or N-methylimidazole in solution in an alcohol ether, for example methoxyethanol.
The reaction is stopped at the desired transformation rate.
The reaction duration is dependent on the structure of the isocyanate, on the dilution, proportion of catalyst, the procedure adopted (batch procedure, continuous procedure . . . ) and the rate of advancement of the desired reaction. That variable time is generally between a few minutes and a few hours, at a maximum 24 hours. The catalysts of the invention permit good control of the reaction and therefore good control of the reaction kinetics and the reaction times.
At the end of the reaction the product obtained comprises in majority terms the following compounds:
the trimer of the initial isocyanate, in particular the xe2x80x9ctrue trimerxe2x80x9d, namely the product of cyclotrimerisation of three molecules of initial isocyanate, comprising an isocyanurate ring;
the dimer of the initial isocyanate, namely the product of cyclotrimerisation of two molecules of initial isocyanate, comprising a uretidinedione ring;
carbamates of the initial isocyanate with an alcohol present in the reaction medium or coming from decomposition of the alcoholate;
allophanates of the initial isocyanate with an alcohol present in the reaction medium or coming from decomposition of the alcoholate;
allophanates, in particular true allophanates, namely the theoretical reaction product of two moles of isocyanate on a mole of alcohol; more precisely the theoretical reaction product of the carbamate formed by the reaction of a mole of isocyanate on a mole of alcohol present in the reaction medium, with a second mole of the initial isocyanate;
bis-trimers, namely the product of tricondensation of two moles of true trimers as defined hereinafter;
heavier oligomeric compounds comprising alone or in mixture isocyanurate, carbamate, allophanate uretidine dione, oxadiazinetrione, imino-oxadiazine-dione functions, in particular heavy trimers, namely the products of condensation of more than two moles of trimers with each other or with another compound present in the reaction medium;
trimer allophanate, namely the product of condensation of a trimer with an isocyanurate function on an alcohol present in the reaction medium to form a carbamate, followed by reaction of the carbamate thus obtained on a supplementary mole of a compound with an isocyanate function; and
unreacted initial monomers.
The procedure does not give a product of nylon type or derivative products resulting from cyclisation of the diisocyanate on itself with consumption of all the isocyanate functions present.
The presence of water in the medium can result in the formation of compounds having urea and/or biuret functions carried, if appropriate, by the structures described hereinbefore.
The advantages of the method essentially lie in mastering and controlling the reaction by way of the use of rare earth catalysts. The advantages of the method thus provide that it is possible to obtain substantial variability in respect of compositions which are desired by the operator to respond to needs for particular properties such as for example low viscosity, and improvement in mechanical properties. It is thus possible to obtain compositions containing a high proportion of true trimers of greater than 50% and compositions containing high proportions of uretdione and isocyanurate compounds when using, in addition to the alcoholate or the mixture of rare earth alcoholate, nitrogenous heterocyclic compounds and the unreacted monomers are eliminated, in particular for isocyanates in which the isocyanate function is carried by a hindered carbon, advantageously secondary, preferably tertiary, and more particularly neopentylic, in particular those of IPDI, with a high rate of transformation of the initial isocyanate, preferably greater than 30%.